Chemical grafting onto a substrate and coating composition

ABSTRACT

A composition and method that provides a chemically grafted coating onto a substrate. The composition comprises an acrylate and a grafting initiator. The acrylate may be a waterborne urethane acrylate. The composition may also comprise resistance agents, adhesion agents, UV curing photoinitators, defoaming agents, and/or deglossing agents. The substrate may be any wood or plastic, but works well with heat shrinkable polyolefin tubing. The composition may also be quick curing such that the coating from the composition may be cured under a D bulb and an H bulb at a rate of 100-160 feet/minute. The coating on the substrate resists delamination and wear. The coating may have indicia printed on the coating, the indicia being composed from ink or other printable materials.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to coatings on a substrate, and, morespecifically, to coatings that do not delaminate from the substrate andto coatings that are capable of receiving indicia.

2. Description of the Related Art

It is generally known in the art that the surface properties of shapedarticles such as polymeric films and fibers can be modified by graftpolymerization processes wherein the article is treated with a freeradical generating agent such as an organic peroxide or high energyradiation and then contacted with an ethylenically unsaturated monomericmaterial under conditions wherein the monomer or graft polymer chain iscaused to be covalently bonded to the substrate.

One particular process involves the treatment of natural or syntheticpolymer substrates containing active hydrogen with an aqueous solutioncontaining a silver salt (silver nitrate), a free radical polymerizationcatalyst and a free radically polymerizable monomer. The silver saltacts upon the substrate to remove active hydrogen thereby creatingactive sites or free radicals along the molecular chain and initiatingand propagating polymerization of the monomer in conjunction with thefree radical polymerization catalyst. The resulting product is a graftcopolymer comprising a substrate having a plurality of polymeric sidechains covalently bonded thereto. Examples of such processes aredisclosed in U.S. Pat. Nos. 3,401,049 and 3,698,931, which areincorporated herein by reference in their entireties. This process issimilar to grafting processes disclosed in U.S. Pat. Nos. 5,342,659;5,439,969; 5,552,472; and 5,741,548, which are incorporated herein byreference in their entireties.

Organic solvent-based coating compositions are known in the art based oncompositions curable by condensation reactions and containing polymericmaterial such as hydroxy terminated polyesters, diesters, acrylics andalkyds and an amino or polyisocyanate crosslinking agent. Theseformulations are adapted to be applied to a substrate such as metal,heated to drive off the solvent and further heated at temperatures above80 degrees C. to activate the crosslinking mechanism.

It is known in the prior art that it is difficult to bond ink to certainsubstrates such as wood-based products and plastics, and even morespecifically to polyolefin. The prior art discloses that the substratesmay be precoated with a material to which the ink bonds. However, theprior art also discloses that the coatings may delaminate or beotherwise removed from the substrate. This is especially true forplastic substrates that are flexible or heat shrinkable, such aspolyolefin tubing.

It is known in the prior art that a substrate may be treated to grow apolymer coating using a process known as chemical grafting. Theresulting coating is covalently bonded to the substrate that isresistant to delamination. Chemical grafting involves the activation ofthe substrate. Once the substrate has been activated, chains of monomerslinked by carbon-carbon bonds grow on the substrate as whiskers. Thesewhiskers impart new and desirable properties to the substrate withoutdamaging any of the existing positive characteristics of the substrate.

The chemical grafting processes relies on the fact that many materials;both naturally occurring and synthetic, possess hydrogens which are moreactive than the “bulk hydrogens.” Examples of relatively more activehydrogens include the tertiary hydrogen in polypropylene, the amidehydrogen in proteins, and the hydroxyl hydrogen in polysaccharide.

The chemical grafting process utilizes graft initiators (GI) that havethe capacity of removing the active hydrogens and initiating the growthof polymer chains at the site of the removed hydrogen. In the case ofpolypropylene, the series of reactions is represented as follows:

A •represents a free radical, anion or cation, depending on whether theGI removes a hydrogen and one electron, no electrons, or two electrons.The below structure:

represents a unit of vinyl monomer where X governs the property orproperties that are obtained with the resulting polymers attached andgrown on the substrate. The graft polymer chains are formed from vinylmonomers or monomers containing appropriate functionability, e.g. groupssuch as hydroxyl, carboxyl, epoxy, amide, amine anhydride. In manyinstances a mixture of monomers is employed and often more than oneproperty can be altered in one processing step. The polymers, whoselength can be controlled, are permanently attached to the substrate. Thelinkage is between the grafted polymer and the substrate is covalent andcannot be leached or otherwise removed from the substrate absentmechanical means such as abrasion.

SUMMARY OF THE INVENTION

In an aspect of the invention, a composition provides a chemicallygrafted coating onto a substrate, wherein the composition comprises anacrylate and a grafting initiator. In further aspects of the invention,the acrylate is a waterborne urethane acrylate.

In further aspects of the invention, the composition comprisesresistance agent, an adhesion agent, a UV curing photoinitator, adefoaming agent, and/or a deglossing agent. The resistance agentincreases the chemical or mechanical resistance of the coating. In stillfurther aspects of the invention, the resistance agent is an acryl-alkydemulsion, a polyether, or a polyethylene glycol diacrylate. In otheraspects of the invention, the adhesion agent is a polyethylene glycoldiacrylate or an ethoxylated trimethylol propane triacrylate monomer. Inadditional aspects of the invention, the UV curing photoinitiator is2-hydroxy-2-methyl-1phenyl-propane-1-one.

In an aspect of the invention, the composition comprises VIAKTIN VTE6155W/50WA at 20-30 parts per weight; RESYDROL VAY 6278W/45WA at 4-5parts per weight; RESYDROL AY 586 W/28 WA at 5-7 parts per weight; BYK024 at 0.1-0.2 parts per weight,; FUJI 370 at 1.5-3.0 parts per weight;SR 344 at 0.12-0.20 parts per weight; de-ionized water at 4-50 parts perweight; ferrous ammonium sulfate (0.1% in de-ionized water) at 0.10-0.15parts per weight; and DARACUR 1173 at 1.2-1.8 parts per weight.

In an aspect of the invention, the composition comprises VIAKTIN VTE6155W/50WA at approximately 28.95 parts per weight; RESYDROL VAY6278W/45WA at approximately 4.45 parts per weight; RESYDROL AY 586 W/28WA at approximately 5.00 parts per weight; BYK 024 at approximately 0.10parts per weight; FUJI 370 at approximately 1.8 parts per weight; SR 344at approximately 0.16 parts per weight; de-ionized water atapproximately 46.00 parts per weight; ferrous ammonium sulfate (0.1% inde-ionized water) at approximately 0.10 parts per weight; and DARACUR1173 at approximately 1.55 parts per weight.

In an aspect of the invention, the composition comprises VIAKTIN VTE6155W/50WA at approximately 28.95 parts per weight; RESYDROL VAY6278W/45WA at approximately 4.45 parts per weight; RESYDROL AY 586 W/28WA at approximately 5.00 parts per weight; BYK 024 at approximately 0.10parts per weight; FUJI 370 at approximately 1.40 parts per weight;SR9035 at approximately 0.20 parts per weight; de-ionized water atapproximately 46.00 parts per weight; ferrous ammonium sulfate (0.1% inde-ionized water) at approximately 0.10 parts per weight; and DARACUR1173 at approximately 1.55 parts per weight.

In an aspect of the invention, the substrate is plastic or wood. In astill further aspect of the invention, the substrate is polyolefin.

In an aspect of the invention, a process for chemically grafting acoating onto a substrate comprising the step of providing a compositioncomprising an urethane acrylate and a grafting initiator along with thestep of coating the substrate with the composition and curing thecomposition coated on the substrate. Further aspects of the inventioninclude a product made by the process and that the substrate is plasticor wood, such as polyolefin for example.

In a further aspect of the invention, the curing step further comprisescuring the composition coated on the substrate under a D bulb and an Hbulb at a rate of 100-160 feet/minute. In a still further aspect of theinvention, a product is made by the process having the step of curingthe composition under the D bulb and the H bulb at the rate of 100-160feet/minute. In an additional aspect of the invention, the substrate ispolyolefin.

In still further aspects of the invention, processes use thecompositions described above and products made with these processes,including having polyolefin as a substrate.

In still further aspects of the invention, the processes include thestep of applying readable indicia onto the coating. In a still furtheraspect of the invention, the readable indicia is ink.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In an embodiment of the invention, a co-polymer, a monomer/prepolymerand a graft initiator are mixed together and coated onto a substrate,such as plastic or wood. The resulting coating is then cured, resultingin a covalently bonded polymer coating on the substrate. In a morepreferred embodiment of the invention, the substrate is flexible, suchas heat shrinkable polyolefin tubing, and the copolymer comprises afunctional group to add flexibility to the bonded polymer coating, withan example of such a functional group being urethane.

In embodiments of the invention, the functional groups of the monomersand prepolymers may consist of hydroxyl groups, carboxyl groups,secondary and/or tertiary amino groups, and epoxy groups. In a preferredembodiment of the invention, the molecular ratio of the reactivecomponents of the mixture are adjusted so that no free groups are leftafter the reaction is complete. Examples of suitable monomers includeethoxylated trimethyl propane triacrylate, polyethylene gycol (400)diacrylate, sodium vinyl sulfate, ethoxylated bisphenol Adimethacrylate, ethoxylated bisphenol A diacrylate, trifunctionalmethacrylate ester, trifunctional acrylate ester, alkoxyated diacrylate.The concentration of the monomers in the solution can vary withinpractically any limits. In a preferred embodiment of the invention, theconcentration of monomers is between about 0.1% and about 50% of theformulation and, more preferably, between about 0.1% and about 20%.

In a step of the reaction, one of the terminal hydrogens of thecopolymer is covalently bonded to the substrate. This is accomplished bythe graft initiator acting as a catalyst. The graft initiator in apreferred embodiment of the invention is ferrous ammonium sulfate whichcontributes the metal ion Fe⁺⁺. Other embodiments of the invention mayuse graft initiators that contribute any other suitable metal ion, suchas Fe⁺⁺⁺, Ag⁺, Co⁺⁺, Cu⁺⁺, and ions of cerium for example. The choice ofthe metal ion depends of the nature of the substrate. In a preferredembodiment of the invention, only a single ion is used as a graftinitiator and not a combination of ions. In a preferred embodiment ofthe invention the graft initiator ion salt concentration may vary in therage of about 0.01% to 0.1% by weight of the monomers.

In an embodiment of the invention, the copolymer comprises ethylenevinyl acetate copolymer (EVA) and/or ethylene ethyl acrylate copolymer(EEA), represented as structures (3) and (4), respectively, below.

The EVA and/or and the EEA is grafted to the substrate and isrepresented as “R-H” in the below structures and reactions. Themechanism of reaction between the EVA and/or the EEA and themonomer/prepolymer is carried out via a free radical mechanism asdisclosed below.

In the first stage of the free radical mechanism, the substrate reactswith the graft initiator (GI) to create the radical:

The propagation of the polymer is then initiated by a monomer bonding tothe radical:

and the polymer propagating therefrom and terminating chain propagationas shown in steps (7) and (8):

“X” represents side functional groups, which may react betweenthemselves and with additional prepolymers or polymers included in themixture. The reaction of the side functional groups may result in thepolymer coating being crosslinked.

A radical combination reaction is used to terminate the polymerpropagation step. In a preferred embodiment of the invention, theradical combination reaction is initiated by a UV curing step. Otherembodiments of the invention may have the free radical produced by anyother suitable means, such as by supplying a peroxide. The peroxidesupplier may be any suitable catalyst, such as benzoyl peroxide, methylethyl ketone peroxide, tert butyl hydroperoxide, hydrogen peroxide, andammonium ferrous sulfate. In an embodiment of the invention, theconcentration of the catalyst may vary in the range of about 0.1% toabout 5.0% of the polymerization solution and, in a preferred embodimentof the invention, between about 0.1% and about 10%.

In embodiments of the invention, the mixture coating may be applied tothe substrate using any suitable method, such a brushing, spraying, anddipping. Embodiments of the invention have mixtures of appropriateproperties for the specific application method. For example, a lowviscosity mixture may be used for a spraying application.

In a preferred embodiment of the invention, ink or another indiciacreating substance is applied to the coating, either before or aftercuring, to dispose readable indicia on the coating surface. The indiciacreating substance may be visible or invisible. The invisible indiciacreating substance may be, for example, machine readable, compriseelectrically charged or magnetically charged particles, emitelectromagnetic wavelengths outside of the visible light wavelengthband, or any other suitable application.

EXAMPLE 1

The formula for the coating mixture according to an embodiment of theinvention is:

Parts INGREDIENTS by Weight VIAKTIN VTE 6155W/50WA 20-30 RESYDROL VAY6278W/45WA 4-5 RESYDROL AY 586 W/28 WA 5-7 BYK 024 0.1-0.2 FUJI 3701.5-3.0 SR 344 0.12-0.20 De-ionized Water  4-50 Ferrous Ammonium Sulfate(0.1% in De-ionized Water)  0.1-0.15 DARACUR 1173 1.2-1.8

VIAKTIN VTE 6155W/50WA is the tradename of a waterborne urethaneacrylate that acts as a binder to the substrate, which in an embodimentof the invention is polyolefin, through chemical grafting. It also formsthe main polymer mix. The urethane part maintains flexibility of thepolymer. RESYDROL VAY 6278W/45WA is the tradename of an acryl-alkydhybrid emulsion that increases the chemical resistance of the polymerand improves its scrub resistance. RESYDROL AY 586W/28WA is thetradename of a polyether that functions as a coalescent for the VIAKTINVTE-6155W/50WA and the RESYDROL VAY 6278W/45WA, which eliminates the useof solvents and improves chemical resistance of the coating. The threeingredients are obtained from Vianova Resins, Inc., Charlotte, N.C.Other embodiments of the invention may use other suitable chemicals fromother suppliers and other embodiments of the invention may only use theurethane acrylate.

BYK 024 is a tradename of a defoamer sold by BYK Chemie USA,Wallingford, Conn. that is mixture of hydrophobic solids and foamdestroying polysiloxanes in polyglycol. Other embodiments of theinvention may not have the defoamer or may have another suitabledefoamer. FUJI 370 is a tradename of a deglossing or flattening agentsold by Fuji Silysia Chemical Ltd., Portland, Oreg., that is silicabased. Other embodiments of the invention may not have a flatteningagent or may have another suitable flattening agent. SR 344 is atradename of a polyethylene glycol (400) diacrylate sold by SartomerCompany, Exton, PAS that promotes adhesion and increases the flexibilityof the coating. Other embodiments of the invention may not have thepolyethylene glycol (400) diacrylate, may have polyethylene glycoldiacrylate of another weight, or may have another suitable chemical thatpromotes adhesion. The ferrous ammonium sulfate is the graft initiator.The Daracur 1173 is a tradename of a 2-hydroxy-2-methyl -1phenyl-propane-1-one sold by Ciba Geigy Chemicals, Tarrytown, N.Y. It isa liquid UV curing photoinitiator for radical polymerization at arelatively high speed of curing. Other embodiments of the invention mayuse another UV curing photoinitator. In a preferred embodiment of theinvention, the coating on the substrate cures under a D bulb and an Hbulb at a speed of 100-160 feet/minute. urethane acrylate coatings inthe prior art cure at a speed of 12-30 feet/minute under similarconditions.

In a preferred embodiment of the invention, the compounding procedure ofthe above formula is to disperse the FUJI 370 into roughly half of theVIAKTIN 6155W/50WA in a high speed mixer, then add the remainder of theVIAKTIN 6155W/50WA and the other ingredients one at a time. After all ofthe ingredients are added to the batch, reduce the speed of the mixerand continue mixing for approximately twenty minutes. The resultingmixture is filtered and drawn off.

VIAKTIN VTE 6155W/50WA is a waterborne urethane acrylate sold by VianovaResins, Inc. Vianva Resins, Inc., Charlotte, N.C., provides this productas a 50% water mixture. The features of VIAKTIN VTE 6155W/50WA include:high film hardness, excellent flexibility, high build, almost noyellowing, stable shear forces, and a milky appearance.

VIAKTIN VTE 6155W/50WA is used in UV or Electron-Beam-Curing (EBC)coating for wood. Application can be by spraying, curtain, or rollercoating. The application viscosity can be adjusted with deionized water.Prior UV or EB-curing all water must be eliminated. Depending on thefilm-thickness, a forced drying step of about 5-10 minutes at 60° C. isrecommended.

Prior to U-V-curing, a suitable photoinitiator must be added (e.g.Nuvopoi Pl 300, Rahn-Chemie, Irgacur 500, CGE 1700, Darocur 1173: CibaGeigy). Its quantity depends on the speed of the conveyor belt, theamount of UV-lamps and the thickness of the coating.

Synthetic resins containing water may freeze or get inhomogenous attemperatures below 0° C. When frozen, the product will not suffer anddamage, but the necessary regeneration requires extended heat treatmentat 40-50° C. with continuous stirring. It is, therefore, recommended toensure frost-proof storage of such products.

At temperatures up to 25° C. and under exclusion of light storagestability of VIAKTIN VTE 6155W/50WA packed in original containersamounts to at least three months.

VIAKTIN VTE 6155W/50WA further has the following characteristics:

Technical Data Unit Value Viscosity mPas 1500-4500 Dynamic viscosity ISO3219/23° C. Cone-and-plate apparatus, sheer rate: 25 s⁻¹ PH-value (10%aqueous solution) 6.4-7.8 DIN 53785/20° C. Density g/cm³ approx 1.06 DIN53217/20° C. Determination of Water Content approx 50% DIN 51777 T1(form of supply) Flash Point ° C. >100 DIN EN 22719 (form of supply)Freeze Stability ° C.   0

RESYDROL VAY 6278W/45WA is an oxidatively drying ammonia neutralizedacrylic alkyd hybrid in aqueous emulsion form. Furthermore, RESYDROL VAY6278W/45WA is an aqueous acrylic alkyd hybrid without organic cosolvents or alkylphenolethoxylates. RESYDROL VAY 6278W/45WA can be usedas a sole binder for decorative paints, wood stains and for industrialapplications. Vianova Resins, Inc., Charlotte, N.C., supplies RESYDROLVAY 6278W/45WA as a 45% water mixture with a fatty acid content ofapproximately 15% (as triglyceride) and neutralized with 0.1% ammonia,as salt.

In comparison to the RESYDROL AY 586W/38WA or RESYDROL AY 430, RESYDROLVAY 6278W/45WA exhibits a quicker drying rate and much less yellowing.Additionally like RESYDROL AY 586W/45WA, VAY 6278W/45WA does not containorganic solvents and therefore is environmentally friendly and has apleasant smell.

Only pigments with very little water-solubility should be used for theproduction of top coats and primers. Strongly basic pigments are notsuitable and may lead to storage stability problems and gelling.Conventional titanium dioxide types (Rutile) without zinc oxide coatingshould give paint with good storage stability. Because of the highmechanical stability of VAY 6278 pearl and sand mills are suitable. Highgloss top coats should utilize a binder-free pigments past for optimumgloss potential. Using Additol VXW 6208 as dispersing agent (5% onpigment) the pigment paste can create systems free of any organicsolvents. RESYDROL VAY 6278W/45WA is also very suitable for theproduction of solvent free wood stains and clear varnishes.

On tannic acid rich woods such as oak or tropical woods like mahogany,drying rate may be delayed and the woods may be discolored, though ourown tests on oak showed no discoloring or retarding of the drying rate.Since RESYDROL VAY 6278W/45WA is highly acrylic modified, optimum dryingrates can be achieved without using driers like Additiol VXW 6206. Usingoptical brighteners like Tint Ayd WD 2018 (Daniel Products) leads tovirtually non yellowing top coats.

Water containing products may freeze and separate at temperatures below0° C. According to tests, RESYDROL VAY 6278W/45WA will not suffer formseveral freeze thaw cycles (a slight increase in viscosity can beobserved). Nevertheless it is recommended to store RESYDROL VAY6278W/45WA away from freezing conditions.

At temperatures up to 25° C. storage stability of RESYDROL VAY6278W/45WA packed in original containers amounts to at least 9 months.

RESYDROL VAY 6278W/45WA also has the following properties:

Technical Data Units Value Dynamic viscosity mPas 100-900 (f.o.d.) DINEN ISO 3219, 23° C. cone-plate apparatus, Shear rate 25 s⁻¹ pH-value7.8-8.6 (10% aqueous solution) DIN 53765, 20° C. Non-Volatile Content %43.5-46.5 Rapid determination (foil method) DIN 55672 (125° C., 10 min)The following are not continuously determined Non-volatile Content %43.5-46.5 DIN EN ISO 3251 (1 g, 125° C., 1 hour) Density g/cm3 ca. 1.03DIN 53217 T3, (20° C.) Flash Point ° C. >100 DIN EN 22719 Note: DIN, ENand ISO are European manufacturing and measurement standards.

EXAMPLE 2

The formula for the coating mixture according to an embodiment of theinvention is:

Parts INGREDIENTS by Weight VIAKTIN VTE 6155W/50WA 28.95 RESYDROL VAY6278W/45WA 4.45 RESYDROL AY 586 W/28 WA 5.00 BYK 024 0.10 FUJI 370 1.80SR 344 0.16 De-ionized Water 46.00 Ferrous Ammonium Sulfate (0.1% inDe-ionized Water) 0.1 DARACUR 1173 1.55

EXAMPLE 3

The formula for the coating mixture according to an embodiment of theinvention is:

Parts INGREDIENTS by Weight VIAKTIN VTE 6155W/50WA 28.95 RESYDROL VAY6278W/45WA 4.45 RESYDROL AY 586 W/28 WA 5.00 BYK 024 0.10 FUJI 370 1.40SR9035 0.20 De-ionized Water 8.00 Ferrous Ammonium Sulfate (0.1% inDe-ionized Water) 0.10 DARACUR 1173 1.55

SR9035 is a tradename of an ethoxylated trimethylol propane triacrylatemonomer that is sold by Sartomer Company, Exton Pa. that introducesflexiblity, chemical resistance, and abrasion resistance besides beingan adhesion promoter.

Although presently preferred embodiments of the present invention havebeen described in detail hereinabove, it should be clearly understoodthat many variations and/or modifications of the basic inventiveconcepts herein taught, which may appear to those skilled in thepertinent art, will still fall within the spirit and scope of thepresent invention, as defined in the appended claims.

What is claimed is:
 1. A composition for providing a chemically graftedcoating onto a substrate, wherein the composition comprises a waterborneurethane acrylate at 20-30 parts per weight; an acryl-alkyd hybridemulsion at 4-5 parts per weight; a polyether at 5-7 parts per weight; adefoamer at 0.1-0.2 parts per weight; a flattening agent at 1.5-3.0parts per weight; a polyethylene glycol (400) diacrylate at 0.12-0.20parts per weight; de-ionized water at 4-50 parts per weight; ferrousammonium sulfate (0.1% in de-ionized water) at 0.10-0.15 parts perweight; and a 2-hydroxy -2-methyl-1-phenyl-propane-1-one at 1.2-1.8parts per weight.
 2. The composition of claim 1, wherein the compositioncomprises of a waterborne urethane acrylate at approximately 28.95 partsper weight; an acryl-alkyd hybrid emulsion at approximately 4.45 partsper weight; a polyether at approximately 5.00 parts per weight; adefoamer at approximately 0.10 parts per weight; a flattening agent atapproximately 1.8 parts per weight; a polyethylene glycol (400)diacrylate at approximately 0.16 parts per weight; de-ionized water atapproximately 46.00 parts per weight; ferrous ammonium sulfate (0.1% inde-ionized water) at approximately 0.10 parts per weight; and a2-hydroxy-2-methyl-1-phenyl-propane-1-one at approximately 1.55 partsper weight.
 3. A composition for providing a chemically grafted coatingonto a substrate, wherein the composition comprises a preparationcomprising a waterborne urethane acrylate at approximately 28.95 partsper weight; an acryl-alkyd hybrid emulsion at approximately 4.45 partsper weight; a polyether at approximately 5.00 parts per weight; adefoamer at approximately 0.10 parts per weight; a flattening agent atapproximately 1.40 parts per weight; an ethoxylated trimethylol propanetriacrylate monomer at approximately 0.20 parts per weight; de-ionizedwater at approximately 46.00 parts per weight; ferrous ammonium sulfate(0.1% in de-ionized water) at approximately 0.10 parts per weight; and a2-hydroxy-2-methyl-1-phenyl-propane-1-one at approximately 1.55 partsper weight.